Hey,for a project I habe to run a 12V device and have to be able to turn on/off it.Is it possible to work without an external power source like a battery? I hope one of you can help me because I have spent a lot of time on searching solutions in the web but couldnt find the right answer!

No, I want to use my arduino to power a 12V converter which convertes to 220V if possible WITHOUT anything like a battery and just need to turn on/off it.

By "use my arduino to power" do you mean using your arduino's regulated power supply, or using the output of one of the arduino's pins to feed into the 12V converter? Is your arduino connected to a battery or a wall source?

Yes, you'll probably want to look at a high-current mosfet transisitor, like those used to drive motors. You could wire the extra supply to a mosfet's source, and then wire an arduino pin to the mosfet's gate to turn it "on" and "off".

You could try wiring that together yourself, but if you're unfamiliar with soldering custom electronics, I would suggest you look at one of the high-power motor control arduino shields.

for a project I habe to run a 12V device and have to be able to turn on/off it.and...I want to use my arduino to power a 12V converter which convertes to 220V if possible WITHOUT anything like a battery and just need to turn on/off it.

By "turn on/off it" do you want to effect the device on/off, power on/off, as with a switch (e.g. a relay)?

"You gotta fight -- for your right -- to party!"Don't react - Read."Who is like unto the beast? who is able to make war with him?"Hey, it's "bipolar transistor" or "junction transistor" - "BJT" is just stupid.